Electromagnetic actuating means for print hammers

ABSTRACT

A print hammer is supported by a cantilever spring and carries a pawl which is actuated by electromagnetic means into the path of teeth on a continuously rotating reamer shaft to impel the hammer to impact a document and a ribbon against type characters on a type chain or the like. Movement of the print hammer resets the armature of the electromagnetic means.

United States Patent 1191 Dayger et al.

[ June 12, 1973 ELECTROMAGNETIC ACTUATING MEANS FOR PRINT HAMMERS [75]Inventors: Jonas E. Dayger, Binghamton;

Albert A. Dowd, Vestal; Joseph A. Vrablic, Binghamton, all of N.Y.

[73] Assignee: International Business Machines Corporation, Armonk, N.Y.

22 Filed: Dec. 28, 1970 21 App1.No.: 101,654

52 U.S.Cl ..101/93c 51 Int. Cl B41] 9/38 58 Field of Search 101/93 0,94, 287,

[56] References Cited UNITED STATES PATENTS 3,152,540 10/1964Pensavecchia et al 101/93 C 3,156,180 11/1964 Barnes .1 101/93 C3,292,531 12/1966 Mutz 101/93 C 3,351,007 11/1967 Poland 101/93 C3,386,376 6/1968 Mutz et al.... 101/93 C 3,447,455 6/1969 Shneider101/93 C 3,499,382 3/1970 Potter et al. l. l0l/93 C PrimaryExaminer--William B. Penn Attorney-Hanifin & Jancin and Francis V.Giolma [57] ABSTRACT 9 Claims, 3 Drawing Figures PAIENIEU 3.738262 sum 2w 2 FIG. 2

ELECTROMAGNETIC ACTUATING MEANS FOR PRINT HAMMERS FIELD OF THE INVENTIONThe invention relates generally to printers and it has reference inparticular to a print hammer mechanism in which the drive is provided bya continuously rotating reamer shaft.

DESCRIPTION OF THE PRIOR ART Print hammer mechanisms using reamer shaftdrives are known such as, for example, described in U. S. Pat. No.3,292,531, whichissued on Dec. 20, 1966, to G. Mutz SUMMARY OF THEINVENTION Generally stated, it is an object of the invention to providean improved print hammer mechanism.

More specifically, it is an object of the invention to provide animproved reamer shaft drive print hammer mechanism.

Another object of the invention is to provide a print hammer mechanismrequiring a minimum of operating power.

Yet another object of the invention is to provide a print hammermechanism having a fail-safe characteristic.

Still another object of the invention is to provide a print hammermechanism requiring a minimum of control circuitry.

It is also an object of the invention to provide a simple and accurateprint hammer operating mechanism.

Another important object of the invention is to provide a print hammermechanism which is consistent and reliable in its operation.

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawing.

DESCRIPTION OF THE DRAWING In the drawing FIG. 1 is a partial schematicview in side elevation and partly sectioned of a print hammer mechanismembodying the inventionin a preferred form,

FIG. 2 is a similar schematic view of a portion of a mechanism shown inFIG. 1 showing the initial drive connection between the print hammer andthe reamer drive shaft, and

FIG. 3 is a similar schematic view of a portion of the mechanism shownin FIG. 1 adjacent the end of the drive connection between the pawl andthe reamer drive shaft with the armature restored to its initial restposition and the print hammer still moving toward the print position.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, a row ofprint hammers represented by the Print Hammer 12 are disposed to impacta Document 13 and Ribbon 14 against moving type extending along theprint line and cooperating with Guide Members 26a and 26b to define arecess through which may travel spaced apart Type Belts 27a and 27bhaving Teeth 28a and 28b, respectively, on the back side for driving thebelts, and arranged in spaced apart relation to receive the TypeElements l6 therebetween. The Type Elements 16 have outwardly extendingfingers on opposite sides defining Recesses 16a and 16b therebetweendisposed to receive edge portions of the Belts 27a and 27b,respectively, fitting exactly between Teeth 28a and 28b on theirrespective belts, for moving the Type Elements 16 along the print line.

The Print Hammer 12 may comprise a Head Portion 12a having a relativelyflat Surface Portion 12b for impacting the Document 13 against the typecharacter bearing Element 16. The Striking Portion 12b is posi-' tionedto one side of the generally cylindrical Body Portion 12a of the hammer,which provides for oscillatively supporting a Pawl Disc 15 in agenerally cylindrical recess defined by arcuate Edge Portions 30a and30b of the Body Portion 12a. The Print Hammer 12 is mounted by means ofHead Support or Flex Pivot 32, which comprises a flat, elongated steelSpring Member 34, molded in a Plastic Body 36, comprising a polymer suchas, for example, Acetal. This spring member provides transverse rigidityand serves as a flexible pivot and return spring for supporting andguiding movement of the Hammer 12 along a predetermined path. ThePlastic Body 36 is notched to provide a Section 37 of reduced thicknessadjacent the Lip 40. This localizes bending or flexing of the Spring 34to the Section 37 of reduced thickness and provides controlled bending,with a reduction in the whipping action often encountered in cantileversprings, resulting in much more uniform print hammer action. The HeadSupport 32 is secured at the lower end by means of a relatively tightfit in a Keyhole Opening 38 adjacent one Lip 40 of a generally C-shapedSupport Plate 42 on which the hammer mechanism is mounted. The upper endof the Head Support 32 is secured to the Print Hammer 12, being securedin any suitable manner in a Slot or Recess 30d therein. A generallyC-shaped Spring 44 biases the Pawl 'Disc 13 in a clockwise directionrelative to the Print Hammer 12. The Pawl Disc 13 is provided with aprojecting Tail Portion 13c to which a Pawl 45 is secured by means of anElastomeric Bond 47, such as Nitrile. The Pawl 45 is disposed so that itmay be activated to engage a Tooth 48 of a Reamer Shaft 49 which iscontinuously rotated. Substantially enclosing the Reamer Shaft 49 is aGuard 50 which is generally cylindrical, but has an Opening 52 throughwhich the Pawl 45 is enabled to engage the Teeth 48. Support Means 53and 53a support the Guard intermediate its ends. The Guard 50 has an EndPortion 54 which serves as a stop and an extractor for the Pawl 45during its normal operation. The Guard 50 is also rotatably mounted andmay be actuated in a counterclockwise direction to restore-the Pawl 45to its rest position, if necessary. A Back Stop 46 mounted on theSupport Means 53a provides a return stop for the Pawl 45 when it isreset.

Selective operation of the Pawl 45 to engage a particular Tooth 48 ofthe Reamer Shaft 49 is effected by Electromagnetic Control Means 56.This comprises a pair of spaced apart Pole Pieces 56a and 56b having aPermanent Magnet 57 positioned therebetween. Operating windings 58a and58b are positioned on extending Pole Portions of the Pole Pieces 56a and56b and are connected by means of Conductors 59 to plug in TypeTerminals 60, which may be molded in the Support Plate 42, which cancomprise any one of the wellknown molded plastic materials. The PolePieces 56a, 5619, Permanent Magnet 57, and Operating Windings 58a and58b may be molded with an enclosing plastic covering to provide anintegral structure. The assembly may be positioned in a Recess 62 in theSupport Plate 42. Cooperating with the Pole Pieces 56a, 56b and theOperating Windings 58a and 58b is an Armature 64 having a Pole Piece 640spanning the Pole Pieces 56a and 56b. The Armature 64 is positioned in aRecess 66 in the Support Plate 42 and has a cylindrical Protuberance640, at one end positioned in a generally C-shaped Bearing Insert 68,embedded in the Support Plate 42 to permit limited rotational movement.The Armature 64 is biased by means of a semicircular Spring 70 locatedat the lower end by the Recess 710 at one end of Recess 71 in theSupport Plate 42 and secured to the Armature 64 by being positioned in arecessed Channel 64d in the lower side of the Armature 64 and furtherrestrained by Recess 64f. The Armature 64 is provided with an extendingTail Piece 64b which extends into a recess in the cylindrical BodyPortion 12a of the Hammer 12 where it may be engaged by anupwardly-projecting Cam Portion 12d of the Hammer 12 for resetting theArmature 64 in response to movement of said Hammer 12 to strike theDocument 13.

Referring to FIG. 1, which illustrates one side of a two-hammer PositionSupport Plate 42, the Permanent Magnet 57 keeps the Armature 64 in anormally attracted position despite the force exerted by the ArmatureSpring 70. While an electromagnet could be used as this holding means,the Permanent Magnet 57 is advantageous because:

.l. It requires no power in the normally long hold periods;

2. Power failure does not cause the Armature 64 to drop therebyinitiating erroneous printing and possibly damaging the Pawl 45 and theReamer Teeth 48 because the Armature 64 would be in a non-hold position;

3. Its smaller dimensions make the'packaging more compact; and

4. No wires or connections are required for the hold circuits, therebysimplifying the wiring of the machine and eliminating troublesomecontacts.

As shown, the Operating Windings 58a and 58b operate as Buck Out Coilswound on the Magnet Pole Pieces 56a and 56b to decrease the holdingforce of the Permanent Magnet 57 when energized, thus permitting theArmature 64 to drop under the action of its Spring 70 and engage Tail 13and Pawl 45 to move the latter into engagement with a Tooth 48 of ReamerShaft 49. The Buck Out Coils 58a and 58b therefore merely have to supplythe difference in power between the forces of the Armature Spring 70 andthe Pennanent Magnet 57 with a reasonable safety factor for properoperation. i

A Pawl Stop 54 is provided on one end of the Guard 50 to limit thetravel of the Armature 64 in the clockwise direction and thereby preventthe Pawl 45 from bottoming between the Teeth 48 of the Reamer Shaft 49.It also minimizes Armature 64 impact on Cam Portion 12d of Hammer 12. Asshown, this Pawl Stop 54 is provided by one end of the generallycylindrical Guard 50 surrounding the Reamer Shaft 49. in addition toproviding the Armature Stop function described, it also serves as ameans for moving the Pawl 45 out of the Reamer Teeth 48 as the Hammer 12moves toward Type Element 16,and as a safety guard on the Reamer Shaft49, as well as providing manual reset for the Armature 64, as will bedescribed later.

The hammer assembly consists of the Print Hammer 12 supported by theHead Support 32, which is attached to the Mounting Plate 42, forming aflexible pivot, which allows the Hammer 12 to swing forward in acounterclockwise direction as it is driven by the Pawl 45. A Cam Surface12d engages the Tail Piece 64b of the Armature 64, as the Hammer 12 isbeing driven forward to impact the Document 13, to reset the Armature bypressing against the inclined surface on the underside of the ArmatureTip 12b, as shown in FIGS. 2 and 3.

When a Reamer Tooth 48 engages the Pawl 45, it drives the Hammer 12forward through the Elastomeric Coupling 47 and the Hammer Pawl Disc 13to which the Pawl 45 is secured. As stated previously, motion of theHammer 12 resets the Armature 64, after which the Hammer 12 fliesforward in free flight, as shown in FIG. 3, driving the Document 13 andRibbon 14 against the Type 16. During rebound of the Hammer 12, the PawlSpring 44 restrains the Pawl 45 against the Armature 64, and as thearmature has been reset, the Pawl 45 clears the teeth of the ReamerShaft 49 as it moves to its normal position. This position is located bya Back Stop 46 which terminates the rebound motion, during which thePawl 45, being urged toward the Armature 64 by the Pawl Return Spring44, latches on the Armature 64 at Shoulder 64a, and thus is preventedfrom rebounding toward the Type 16. The Elastomeric Coupling 47 of thePawl 45 and Hammer 12 (which may comprise rubber or a rubberlikecomposition) serves three purposes:

1. When the Armature 64 drops the Pawl 45, it strikes against the PawlStop 54 and the Elastomeric Coupling 47 goes into compression, servingas a damping means to prevent rebound;

2. When the Reamer Tooth 48 strikes the Pawl 45, the design of theElastomer 47 is such that the Pawl 45 stays in contact with the ReamerTooth 48 instead of taking offlike a baseball being struck by a bat. Thepurpose of this action is to keep the Pawl 45 under control of theReamer Shaft 49 within the area of potential contact with one another;and

3. When the Pawl 45 strikes the Back Stop 46 in the rebound operationafter printing, the Elastomer 47 is again compressed and serves adamping agent which allows the Pawl 45 to latch properly with theArmature 64.

Should, through some malfunction, the Armature 64 fail to hold duringits restoring operation, the Projection 64b of the Armature 64 will dropbehind the restoring Cam Surface 12d in the Head 30 thereby preventingthe Hammer 12 and its Pawl 45 from returning from its normal position.This feature is supplied to prevent repeated erroneous printing anddamage to the Pawl 45 or the Reamer Teeth 48 by the Armature 64 beingincorrectly in a released position. In order to manually restore theHammer 12, the Pawl Stop 54 or Guard Ring 50, which is located in aCounterbore 51a in an End Support Plate'50, is rotated in acounterclockwise direction. This forces the Armature 64 to the restoreposition, which will allow the Hammer 12 to return to its normalposition. Means such as the Spring 53- may be provided to bias the Guard50 clockwise to the position shown against a Stop as at 50a. Should theArmature 64 still fail to hold, the Armature 64 will again latch behindthe Head of the Hammer 12 after the next Reamer Tooth engagement. Such acondition would be most unusual and would require a manual intervention.

In order to insure precise location of Hammer Face 12b at time of Typeimpact, a Projection l2e on one side of the Hammer 12 rides in acomb-like Guide 72 as it moves in towards the Paper or Document 13. ThisProjection l2e serves to engage an impression control comprising aSpring Finger 73, which increasingly limits the force delivered to formsless than six parts, but does not engage when a six-part form is to beprinted. With the type faces at a constant level, the variation in formsthickness automatically determines the amount of impression control.This Impression Control 73 has a second function, which is to insurethat the Hammer 12 strikes the Type 16 squarely on the forms ofdifferent thicknesses by rotating the hammer head slightly to preciselycompensate for different angular motions of the head caused by thepivoted hammers striking different thicknesses against a fixed typelevel. From the above description and the accompanying drawing it willbe apparent that the present invention has the following advantages:

l. The use of a Reamer Shaft 49 permits variations in armature droptiming which would otherwise cause serious misregistration at the speedsthe machine is operating. Variations ofi 0.350 microseconds can beaccepted with the Pawl 45 still dropping into the proper tooth and withthe Hammer 12 being driven in proper relation to the type motion.Therefore, no flight time adjustments are needed;

2. The power for resetting the Armature 64 is supplied by the ReamerShaft 49 as the coupling design prevents the Pawl 45 from leaving theTooth 48 until the reset operation is practically complete;

3. After armature restoration, the Hammer 12 continues in free flightwith the momentum and energy determined by the mass of the hammerassembly and the velocity of the Reamer Shaft 49. It is believed thathigher energy and momentum are possible with this design over thatobtainable with magnetically-driven hammers;

4. The extremely short actuating impulse to the Buck Out Coils 58a and58b (less than 300 microseconds) permits a matrix drive arrangement ofthe electronic driving circuits (not shown). For example, 40 drivers areused to control 144 hammers.

5. The design permitsthe mounting of the hammers and magnets in a singlerow at to the inch spacing. The Hammer Plate 42 carries 2 hammermechanisms, one on each side, on 0.100 inch centers conveniently mountedin a plug-in mode with all hammer wiring being carried by printedcircuits in the plug-in receptacle. These plates are identical for allprint positions;

6. The power required by the Buck Out Coils 58a and 58b is far less thannormally required to actuate a hammer position with conventional workmagnets;

7. The Reamer Shaft 49 provides unlimited continuous power for drivingthe Hammers l2;

8. By using an Interposer Pawl 45 for hammer driving, a small, lightmass is moved a short distance for rapid operation;

9. The mass of the hammer head is concentrated behind the Impacting Face12b giving a maximum effective mass to the print head;

10. The Hammer Head 12a is supported by a Head Support 32 which consistsof a Spring Member 34 reinforced by a polymer such as Acetal so thatflexure is 10- calized at an optimum point and oscillations in thebalance of the spring are minimized. The polymer serves the additionalpurpose of anchoring the head to the spring and the spring to thesupport plate;

1 I. All major forces pass through the center of mass of the hammerhead, thus minimizing oscillation caused by eccentric forces; and

12. Reamer elements are identical one-position modules, comprisingindividual toothed discs, which are staggered one-quarter tooth so as toprovide sequential firing of groups of print hammers in synchronism withType Elements 16 whose pitch is such that only every fourth Type Elementis in position for printing at any time. This staggering may beaccomplished by providing four different key ways in each element.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. In a printer having means for moving a plurality of type characterbearing elements along a print line adjacent a document on which aprinting operation is to be performed,

a print hammer movable to impact said document and type characterbearing elements for printing on said document,

a single spring support having a localized bending zone connected tosaid print hammer for supporting said print hammer in an initialposition and guiding said hammer for movement relative to said document,

a continuously rotating reamer shaft disposed adjacent said print hammerand having a plurality of peripheral pawl means carried by said printhammer movable from a normal position to engage a tooth of said reamershaft to impel said hammer toward said document,

and electromagnetic control means having an armature operable to engageand move said pawl means from said normal position to a tooth engagingposition for moving said print hammer to impact said document and typecharacter bearing elements and said electromagnetic control means havinga control winding disposed to be pulsed to effect operation of saidarmature.

2. The invention as defined in claim 1 characterized by said printhammer spring support comprising a cantilever spring having a reducedsection to localize bending.

3. The invention as defined in claim 2 characterized by said cantileverspring comprising a flat metallic spring element molded in a polymerplastic body having said reduced section.

4. The invention as defined in claim 3 characterized by said pawl meanscomprising a pawl mounted on a pawl support which is oscillativelymounted on said cantilever spring.

5. The invention as defined in claim 4 further characterized by saidpawl being pivotally mounted on said pawl support.

6. The invention as defined in claim characterized by said pivotalmounting comprising an elastomeric bond providing a resilient dampedconnection between the pawl and said pawl support.

7. The invention as defined in claim 3 characterized by spring meansbiasing said armature toward said pawl means, said electromagnet controlmeans including a permanent magnet for holding said armature in aninitial set position against the bias of said spring means and a controlwinding disposed to be energized to reduce the holding force of saidpermanent magnet and permit said spring to bias said armature to movesaid pawl means into engagement with a tooth on said reamer shaft, and acam portion on the print hammer positioned to engage a portion of saidarmature when said print hammer is impelled toward said document torestore said armature to said initial set position.

8. The invention as defined in claim 6 characterized by a guard membersubstantially surrounding said reamer shaft and having a cam surfacepositioned to engage said pawl as said hammer approaches the printposition, said cam surface lifting said pawl out of engagement with saidreamer, and said guard ring being manually rotatable to actuate saidarmature to said initial set position.

9. The invention as defined in claim 7 characterized by said armatureextension engaging said cam portion of said print hammer to preventreturn of said print hammer to its initial position until said armatureis restored to its said set position.

1. In a printer having means for moving a plurality of type characterbearing elements along a print line adjacent a document on which aprinting operation is to be performed, a print hammer movable to impactsaid document and type character bearing elements for printing on saiddocument, a single spring support having a localized bending zoneconnected to said print hammer for supporting said print hammer in aninitial position and guiding said hammer for movement relative to saiddocument, a continuously rotating reamer shaft disposed adjacent saidprint hammer and having a plurality of peripheral pawl means carried bysaid print hammer movable from a normal position to engage a tooth ofsaid reamer shaft to impel said hammer toward said document, andelectromagnetic control means having an armature operable to engage andmove said pawl means from said normal position to a tooth engagingposition for moving said print hammer to impact said document and typecharacter bearing elements and said electromagnetic control means havinga control winding disposed to be pulsed to effect operation of saidarmature.
 2. The invention as defined in claim 1 characterized by saidprint hammer spring support comprising a cantilever spring having areduced section to localize bending.
 3. The invention as defined inclaim 2 characterized by said cantilever spring comprising a flatmetallic spring element molded in a polymer plastic body having saidreduced section.
 4. The invention as defined in claim 3 characterized bysaid pawl means comprising a pawl mounted on a pawl support which isoscillatively mounted on said cantilever spring.
 5. The invention asdefined in claim 4 further characterized by said pawl being pivotallymounted on said pawl support.
 6. The invention as defined in claim 5characterized by said pivotal mounting comprising an elastomeric bondproviding a resilient damped connection between the pawl and said pawlsupport.
 7. The invention as defined in claim 3 characterized by springmeans biasing said armature toward said pawl means, said electromagnetcontrol means including a permanent magnet for holding said armature inan initial set position against the bias of said spring means and acontrol winding disposed to be energized to reduce the holding force ofsaid permanent magnet and permit said spring to bias said armature tomove said pawl means into engagement with a tooth on said reamer shaft,and a cam portion on the print hammer positioned to engage a portion ofsaid armature when said print hammer is impelled toward said document torestore said armature to said initial set position.
 8. The invention asdefined in claim 6 characterized by a guard member substantiallysurrounding said reamer shaft and having a cam surface positioned toengage said pawl as said hammer approaches the print position, said camsurface lifting said pawl out of engagement with said reamer, and saidguard ring being manually rotatable to actuate said armature to saidinitial set position.
 9. The invention as defined in claim 7characterized by said armature extension engaging said cam portion ofsaid print hammer to prevent return of said print hammer to its initialposition until said armature is restored to its said set position.